First of all I am not sure about your problem...i notice there is libreoffice-3.5.4 in the testing repo maybe you can try that...If you run libreoffice from terminal...is there any error from terminal when the problem happen?have you try any luck in the libreoffice forum or irc channel?

I installed LibreOffice just a while ago, and I found that it worked okay, but did screw up some little tasks, like correctly printing an envelope, that I was able to reliably do on OpenOffice.org. So, my advice is to dump LibraOffice for OpenOffice.org, and see if that works better. Or, join a mailing list of theirs and see if you can find an answer with other users.